Field of the Invention
The present invention relates to an endoscope optical system unit.
Description of the Related Art
An endoscope is an apparatus that has been used widely in a medical field and an industrial field. Particularly, in the medical field, images of various parts inside a body cavity are captured by an endoscope inserted into the body cavity. A diagnosis of a part observed, is carried out by these images. In such manner, endoscopes have been used for observation and diagnosis of various body parts inside the body cavity.
A non-bending variable visual-field endoscope in which it is possible to change a direction of observation by driving an optical element at an interior of an objective optical system without bending an inserting section at the time of observing various parts inside the body cavity, has been known.
In the observation by such variable visual-field endoscope, it is desirable that a subject image in any direction of observation that can be achieved in the objective optical system can be observed with adequate brightness.
Illuminating in advance, regions in all directions of a range of variable visual-field for fulfilling the requirement may be taken into consideration. However, a range to be illuminated being wide, it is difficult to illuminate with uniform intensity in all directions. As a result, problems such as change in the brightness of subject according to the visual-field direction and uneven brightness in the subject image arise.
As another arrangement for fulfilling the requirement, an illuminating optical system proposed in Japanese Patent No. 4458211 Publication for example, has been known. In the illuminating optical system of Patent Literature 1, by making it possible to drive one optical element at an interior of the illuminating optical system, irradiation of illumination light followed by the movement of the objective optical system in the visual-field direction is made possible. With this arrangement, it is possible to illuminate uniformly in any visual-field direction, and furthermore, since it is possible to narrow a range to be illuminated at a time, the unevenness in brightness of a subject image is not susceptible to occur.